Define “Normal”

We had a great Hello Doc question from a reader*:

Could you define “normal”?

Luckily for Doc Gurley, this question wasn’t a request for a metaphysical definition of human non-weirdness (Doc Gurley, in fact, loves human weirdness), but was, instead, a medical question. In other words, our reader continues –

I had my vitamin D tested in September – it was 17 – and I then started taking 1000 IUs of vitamin D a day. In three months, it went up to 33, but is that still too low?”

So what should your vitamin D blood level be? What is “normal”? You would think that question should have an easy answer, right? Most of us

Parathyroid hormone
Image via Wikipedia

think of it as Body Algebra: if your blood level is X, then should it be Y?

Well, when it comes to vitamin D (and many other lab tests) the answer is actually a bit more complicated than that. Instead of a simple equation like if X, then Y (why?why?), your question’s math is actually more like…If a train is going northwest 40mph and a fly goes 0.001 metric tons south-yards over a bowl of soup (ick-factor = 7.9 depth charges), then how fast does the waiter’s fly-swat need to torque (twitches/nmol)? Sadly, it’s almost that bad when it comes to answering your question. Why? And really, what the heck is normal? Well, grab a cup of coffee and here goes:

First, most laboratories that test blood results base their “normal” on the masses of other people being tested. In other words, normal is an average (or, to be even more specifically geeky, a median) – a number that includes the people who got tested because someone thought it might be low, plus the many, many people in this country (for example – 80% of African Americans) who we already know are likely to have very very low vitamin D levels. A “normal” blood cut-off for anemia in a lab that tests mostly male smokers will be higher than a lab that tests mostly non-smoking young women (smoking = carbon monoxide = higher red blood counts; young women = menstruating = lower blood counts). What that means is that “normal” for most lab results of vitamin D is actually, well, still low.

So what should “normal” be? With vitamin D, there are three choices – the first is to look at the blood values of people who are still living that way we humans lived 2-3 generations ago. For those people (tropical workers whose jobs are mostly outdoors), their vitamin D levels are much higher than our lab’s “normal.”

The second option is to base normal on a marker in your body – in this case, a hormone called parathyroid hormone (or PTH). The reason PTH is used is because it’s kind of a distress signal for when your body is not getting enough of the all-important calcium+vitamin D combo. Your PTH starts to go up long before your vitamin D level drops to a lab-defined “normal.” So “normal,” based on both these factors, probably ought to be higher than what your lab, or your doctor (unless your doctor is unusually aware of this issue), thinks.

The third way to look at normal is to try to find a number where people in studies have done the best overall – in other words, how high did your vitamin D have to be before a large group of people were protected (or didn’t get) some nasty things that are associated with low vitamin D? Again, that number is higher than the usual “normal” number for labs (and doctors).

Are you with me so far – or have you been forced to get toothpicks to prop open your eyelids?

All of this brings us to our second, annoying factor about defining “normal” – there are two different ways of reporting vitamin D levels: either as ng/ml or nmol/L. Sheesh. In this case, we’ve got apples and oranges – and it’s really important to know which you’re talking about. If your numbers are ng/ml – a less common way of reporting – then your “normal” would generally be above 30. But an optimum normal would be, based on many thoughtful and informed opinions, more like 40. But if your lab numbers are the nmol/L kind, the goal for optimum health would be a number of 80 (although studies with the VA show a level of 90 is necessary to prevent tooth loss…). With either “unit of measure” (as we like to pompously call the ng/ml vs. nmol/L issue), your blood level is still LOW. And, I personally might add, it’s taking a wee bit too long for it to come up appropriately (it’s been over 6 months). So what’s an informed body-owner to do?

First, keep in mind that what you’re experiencing is not unusual – many many people (if not most) need much more than 1,000 units a day to get to a normal (however you define it) blood level of vitamin D. Then, when you’re stable at a decent blood value for more than one test, you’ll need to keep taking it the rest of your life.

Second, your doctor probably needs some coaching on this subject. It is horrifying how little doctors are taught about this very important topic (moi included).

Finally, you can definitely take too much vitamin D. Waaay more is not better. If you’re taking less than 10,000 units a day, you’re probably going to be okay – as long as you don’t have a history of (among other things) kidney stones, sarcoidosis or a disease called primary hyperparathyroidism. If your doctor suggests you take 50,000 units once a week, that’s okay too – but keep in mind that the vitamin D overdoses that have been documented (and were very serious, requiring hospitalization) have often been because of medical errors using the hyper-concentrated 50,000 unit stuff – so take it carefully and be sure you’re NOT taking IT every day (once a week = okay; every day = NOT).

And what did our reader reply? In fact, the range for normal from the first lab test was 32-100. But then the doctor changed labs, and the second lab’s range of normal was 20-100, proving Doc Gurley’s point about lab averages.

Bottom line? Pick a “normal” for vitamin D that makes sense for your health, not one based on an average of other people – many or most of whom are low.

*Got a question for Doc Gurley? Remember to see your own doctor for specific medical advice, but if you’ve got a puzzler on a general topic, ask away by emailing her – not all questions will be chosen, but any identifying information will be stripped if it’s published!

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